In order to rotatably support vehicle wheels of an automobile with a suspension device, a rolling bearing unit with an encoder 1 illustrated in FIGS. 9 and 10 is widely known in the related art (for example, see Patent Documents 1 and 2). In the rolling bearing unit with an encoder 1, an outer ring 2 which is an outer race member and a hub 3 which is an inner race member are arranged to be coaxial with each other. Plural balls 6 and 6 which are rolling elements are between double-row outer raceways 4 and 4 formed on the inner circumferential surface of the outer ring 2 and double-row inner raceways 5 and 5 formed on the outer circumferential surface of the hub 3 for each row. The balls 6 and 6 are held by retainers 7 and 7 so as to be rollable. With this configuration, the hub 3 is rotatably supported inside the outer ring 2 which is supported by and fixed to a suspension device.
Between the inner circumferential surface of the outer ring 2 and the outer circumferential surface of the hub 3, both axial end openings of an annular space 8 in which the balls 6 and 6 are located are seal off by a seal ring 9 and a combined seal ring with an encoder 10 over the entire circumference thereof. The seal ring 9 includes a metal insert 11 formed by a metal plate and plural seal lips 12 formed by an elastic member. The tip edges of the seal lips 12 are brought into sliding contact with the outer circumferential surface of an axially intermediate portion of the hub 3 over the entire circumference in a state in which the metal insert 11 is internally fitted and fixed to the axially outboard end portion of the outer ring 2 by tight fit (The outboard in the axial direction indicates the left side in the drawings on the outboard in the width direction of a vehicle body in an assembled state into an automobile. On the contrary, the inboard in the width direction which is the right side in the drawings is indicated by the inboard in the axial direction. This definition is true of the entire specification).
The combined seal ring with an encoder 10 includes a seal ring 14 and a slinger 15 composing a combined seal ring 13 and an encoder 16. The seal ring 14 includes a metal insert 17 with an L-shaped cross-section which has an annular shape as a whole and an elastic member 18. The metal insert 17 is obtained by forming a metal plate such as a mild steel plate in an L cross-sectional shape and in an annular shape as a whole. The metal insert 17 includes a fixed cylindrical portion 19 which is internally fitted to the inner circumferential surface of an axial inner end portion of the outer ring 2 by tight fit and a fixed circular ring portion 20 which is bent inward in the radial direction from an axially outboard end edge of the fixed cylindrical portion 19 toward the outer circumferential surface of the hub 3. The elastic member 18 is bonded to the entire circumference of the metal insert 17 and includes one or more (three in the illustrated example) seal lips 21a to 21c. In general, the elastic member 18 is formed by rubber and is fixed to the metal insert 17 by baking.
On the other hand, the slinger 15 includes a rotating cylindrical portion 22 which is externally fitted and fixed to the outer circumferential surface of an axially inboard end portion of the hub 3 (an inner ring constituting the hub 3 along with a hub body) by tight fit and a rotating circular ring portion 23 which is bent outward in the radial direction from an axially inboard end edge of the rotating cylindrical portion 22 to the inner circumferential surface of the outer ring 2. In the slinger 15, portions which are brought into sliding contact with the tip edges of the seal lips 21a to 21c on the outer circumferential surface of the rotating cylindrical portion 22 and the axially outboard side surface of the rotating circular ring portion 23 have smooth surfaces.
The encoder 16 is formed by a permanent magnet such as a rubber magnet or a plastic magnet and is magnetized in the axial direction. The magnetization direction is made to vary alternately at equal intervals in the circumferential direction. Accordingly, on an axially inboard surface of the encoder 16 which is a detection target surface, an S pole and an N pole are arranged alternately at equal intervals in the circumferential direction. The detection target surface of the encoder 16 is set to face a detection unit of a sensor so as to measure a rotation speed of a vehicle wheel rotating along with the hub 3. A signal indicating the measured rotation speed of the vehicle wheel is used to control a driving stabilizing system of a vehicle such as an anti-lock brake system (ABS) or a traction control system (TCS).
In a first example having the above-mentioned structure in the related art, the combined seal ring with an encoder 10 can effectively prevent entrance of relatively large substance such as dust, but has difficulty in reliably preventing intrusion of rainwater, muddy slurry, or the like. That is, in the combined seal ring with an encoder 10, the rotating cylindrical portion 22 of the slinger 15 is externally fitted and fixed to the outer circumferential surface of the axially inboard end portion of the hub 3, and a structure for sealing the fitting part is not formed. Even in a state in which the rotating cylindrical portion 22 of the slinger 15 is externally fitted to the outer circumferential surface of the axially inboard end portion of the hub 3 by tight fit, it is not possible to avoid generation of a minute clearance in the fitting part. When moisture intrudes into the minute clearance, at least one circumferential surface of both circumferential surfaces is corroded and thus the volume of that part is increased and the minute clearance is enlarged. There is a possibility that moisture will intrude into an annular space 8 through the enlarged clearance. The intrusion of moisture into the annular space 8 causes degradation in durability of the bearing unit due to degradation of a lubricant, which is not desirable. Similarly, it is difficult to satisfactorily secure sealability of the fitting part using only the combined seal ring with an encoder 10 having the above-mentioned structure in the related art.
For the purpose of prevention of the above-mentioned intrusion of rainwater or the like into the annular space, for example, Patent Document 3 proposes use of an combined seal ring with an encoder 10a illustrated in FIG. 11. In the second example having this structure, a lip portion 24 having an inner diameter smaller than the inner diameter of a rotating cylindrical portion 22a of a slinger 15a is formed in the inner circumferential edge portion of an encoder 16a. In a state in which the rotating cylindrical portion 22a of the slinger 15a is externally fitted and fixed to a hub 3a, the lip portion 24 is brought into elastic contact with the outer circumferential surface of the hub 3a. 
However, in the second example having the above-mentioned structure, it is difficult to satisfactorily secure sealability of the fitting part of the rotating cylindrical portion 22a of the slinger 15a and the outer circumferential surface of the hub 3a for the following reasons. That is, since the material of the lip portion 24 is the same as the material of the encoder 16a and includes a lot of ferromagnetic material such as ferrite (for example, 80 wt % to 90 wt %) to secure sufficient magnetism, the lip portion is less likely to be elastically deformed and more fragile than a general sealing material. On the other hand, the encoder 16a is formed by disposing the slinger 15a in a molding die (mold) and fixing (fixing by vulcanization or injection molding) a permanent magnet material (a polymer material such as rubber or synthetic resin containing a ferromagnetic material) which will be a permanent magnet to the slinger 15a. When the encoder 16a is formed in this way, a portion which will be the lip portion 24 has to be deformed greatly (has to be forced extraction) depending on the magnitude of an interference in pulling out the slinger 15a and the solidified permanent material (non-magnetized encoder) from the molding die. Since it is difficult to greatly deform the portion which will be the lip portion 24 in this way, it is difficult to secure the interference of the lip portion 24 to be great. When the rotating cylindrical portion 22a of the slinger 15a is externally fitted and fixed to the hub 3a by tight fit, the rotating cylindrical portion 22a is elastically enlarged in diameter, but the rotating cylindrical portion 22a and the rotating circular ring portion 23a are formed continuous and thus the influence of the enlargement in diameter of the rotating cylindrical portion 22a is likely to be transmitted to the rotating circular ring portion 23a. Accordingly, the encoder 16a supported and fixed to the rotating circular ring portion 23a is likely to be enlarged in diameter and a decrease in interference of the lip portion 24 increases. In case of the sealing structure using the lip portion 24, the magnitude of its bending deformation affects the magnitude of a tightening force. Accordingly, without securing the great interference to increase the bending deformation, it is not possible to secure a satisfactory tightening force. However, since the material of the lip portion 24 is not likely to be elastically deformed, it is difficult to secure a satisfactory tightening force in spite of securing of the interference. As a result, even in the second example having the above-mentioned structure, it is difficult to satisfactorily secure sealability of the fitting part of the rotating cylindrical portion 22a of the slinger 15a and the outer circumferential surface of the hub 3a. 